Many burner control systems, particularly those that operate automatically or unattended, are protected by a number of different interlock switches which monitor particular conditions in the burner system and which shut down the system if a dangerous condition is detected by one or more of the switches. Frequently, during the shutdown procedure, one or more of the monitored conditions will change such that the associated interlock switch also opens. It is also not uncommon for an interlock switch to open momentarily and then reclose. If the cause of the failure is intermitent or only appears during operation, it may be very difficult to determine what caused the shutdown or how to correct the condition.
Systems are known which monitor a number of interlock switches and detect which of the switches first opens to shut down a system. One example of such a system is the type 53SE1 System Indicator, manufactured by the Electronics Corporation of America.
In starting up a burner control system, a number of operations occur in sequence during the ignition of a pilot flame and a main flame. During the start-up sequence, the burner control system may shut down the furnace in response to failures which are not normally monitored by means of interlock switches during the main burner operation. Frequently, during the shutdown of a furnace during the start-up procedure, an interlock switch will open. If the interlock switches are monitored by a typical, prior art circuit, this circuit will indicate that that interlock switch was first activated. This may provide an erroneous indication of the source of the failure, since the failure may actually have occurred in a part of the burner not monitored by interlock switches. Thus, such a system may, in fact, mislead a person who is attempting to determine the cause of the furnace failure.